1. Field of the Invention
The present invention relates to a flattening method and a flattening apparatus, and more particularly to a flattening method and a flattening apparatus for flatly processing a surface (surface to be processed) of a workpiece, such as a simple substrate consisting of SiC or GaN, a bonded substrate (epitaxial substrate) having a layer of SiC or GaN, or a substrate for use in MEMS (micro electro mechanical system).
2. Description of the Related Art
With the recent progress toward higher integration of semiconductor devices, the circuit interconnects are becoming finer and the distance between adjacent interconnects is becoming smaller. Especially when forming a circuit pattern by optical lithography with a line width of not more than 0.5 μm, a stepper requires a high flatness of imaging surface because of the small depth of focus. A CMP apparatus for carrying out chemical mechanical polishing (CMP) is known as a means for flattening a surface of such a semiconductor substrate.
SiC, GaN, etc. are becoming increasingly important as a material for semiconductor devices. As a new processing method for flatly processing with high precision a surface of SiC or GaN, a CARE (catalyst-referred etching) method has been proposed which utilizes a catalytic action, capable of a chemical reaction, to etch a surface of a workpiece. The CARE method comprises immersing a workpiece in a processing solution containing hydrohalic acid, such as hydrofluoric acid; placing a platinum, gold or ceramic solid catalyst in contact with or close proximity to a surface (surface to be processed) of the workpiece so as to cause molecular dissociation of hydrogen halide at the surface of the catalyst, thereby generating a halogen radical; and dissolving a halogen compound, which has been produced by chemical reaction between the halogen radical and a surface atom of the workpiece, in the processing solution. The surface of the workpiece is processed (etched) in this manner (see e.g., Japanese Patent Laid-Open Publication No. 2006-114632).